A surface acoustic wave device, which is an electromechanical transducer device utilizing surface waves propagated on the surface of an elastic body, has a general structure shown in FIG. 1, for example. In such a surface acoustic wave device 30, a piezoelectric phenomenon which is caused by a piezoelectric material 31 is utilized for generating surface waves. When an electric signal is applied to one of the interdigital electrodes 32 provided on the piezoelectric body 31, strains are generated in the piezoelectric body 31, which cause surface acoustic waves propagated on the piezoelectric body 31 converting said waves into an electric signal available at the other one of the interdigital electrodes 33. The term "interdigital" as used herein means that the electrodes forming a pair have finger-like extensions that intermesh with each other as shown in FIG. 1. The frequency characteristics of a device have the bandpass characteristics with the frequency f.sub.0 at the center of the band, which frequency is determined as f.sub.0 =v/.lambda..sub.0 where .lambda..sub.0 represents the period of the electrodes of the interdigital electrodes and v represents the velocity of the surface acoustic waves.
The surface acoustic wave device can be used as a filter, a delay line, an oscillator, a resonator, a convolver, a correlator and so on. Especially, a surface acoustic wave filter has been practically used as an intermediate frequency filter in a television for a long time. Such devices are now being used as filters for VTR and various kinds of communication devices.
With respect to the above described surface acoustic wave device, a device which can be operated at a higher frequency range has been desired as a surface acoustic wave filter used in the field of mobile communication, for example. As shown by the above equation, if the period .lambda..sub.0 of the electrodes is made smaller or if the velocity v of the surface waves is made higher, the frequency characteristics of the device would have a higher center frequency f.sub.0. Japanese Patent Laying-Open No. 64-62911 commonly owned by the assignee of this application discloses a surface acoustic wave device in which a piezoelectric body is stacked on a diamond layer so as to increase the velocity v of the surface acoustic waves. The sound velocity in diamond is the highest compared to all materials known at present, and diamond is physically and chemically stable. Namely, diamond is a material suitable for increasing f.sub.0 of the device with a high reliability.
Interdigital electrodes have been formed by photolithography. When a photolithography technique is employed, it is difficult to make the electrode width smaller than about 0.5 .mu.m because of technical limits of photolithographic fine processing. The frequency f.sub.0 of the device can be increased by using diamond as mentioned above, and it is necessary to reduce the electrode width to make the period .lambda..sub.0 of the electrodes smaller, if a still higher frequency f.sub.0 is desired.